Optical field inscription for dark pulse generation

Dark pulses, valued for their robustness against environmental perturbations, are attractive for optical communication and sensing. However, the current mainstream approaches for dark pulse generation face key limitations: nonlinear Schrödinger equation (NLSE)-driven dark solitons require dispersive media in fiber links, and domain-wall dark pulses are confined to fiber lasers. To address these limitations, we introduce an optical field inscription technique for generating dark pulses in the negative group velocity dispersion (GVD) regime. In this method, a mode-locked bright soliton from a 1550-nm fiber laser is dechirped to a transform-limited pulse, which serves as the seed pulse. A temporal hyperbolic tangent-like profile with a π-phase jump is then inscribed at the center of a chirp-free seed pulse via online optical field modulation. The inscribed pulse is subsequently expanded into a dispersion-scaled dark pulse structure. This structure retains the characteristic π-phase jump and intensity-dip signature of a dark soliton, but its ns-scale structure is determined by linear stretching rather than by the balance of dispersion and nonlinearity. Experimental results show excellent agreement with theoretical predictions of the inscription process. Different dark pulse patterns, i.e., black and gray pulses, can be dynamically achieved by adjusting inscription widths. This work establishes a dynamic, dispersion-independent route for programmable dark pulse generation, with potential impact on reconfigurable optical communication and sensing systems.